Surgeons typically wear face masks designed primarily to prevent contamination of the surgical field and wound by bacteria and other infectious particles borne in the surgeon's breath and on the face and facial hair. These masks generally cover the wearer's nose, mouth, chin, and medial aspects of the cheeks. Formerly, these were made of cloth and were washed, sterilized, and reused many times. The era of comparatively inexpensive disposable materials led to these masks being made of some type of paper (cellulosic) fiber or combination of thermoplastic films and fibers and thus becoming single-use, disposable items.
A commonly used mask features a horizontally pleated rectangle of porous paper with 12"-14" (30.5-35.6 cm) long paper-string tie strands at each corner. The tie strings are used to tie the mask behind the neck and over the top of the head of the wearer. The lateral edges of the mask usually conform rather loosely to the sides of the wearer's cheeks. This fit is dependent on the tightness to which the wearer ties the strands, whether the mask is tied according to the intent of the design, and the general shape of the wearer's face. Bands of thin metal or other malleable material are often fabricated into the upper edge of the mask to allow molding of this edge to the contour of the upper nose.
Masks of this invention preferably are made of somewhat permeable material, in that expired air may pass through the mask, ideally filtering out aerosol particles in the expired air to prevent their contaminating the surgical wound. However, if the mask is not applied according to design; if the wearer ties the strands loosely; if the malleable band is not molded to the contour of the upper nose; or if the wearer's face is particularly thin, there may be relatively free flow of air around the edges of the mask. Commonly, a substantial portion of the air expired by the wearer passes out around the mask, generally at either side and out the upper edge, as the mask fits rather loosely and is not sealed to the wearer's skin. This is associated with at least three problems:
1) the exhausting of expired air around the edges of the mask exposes the surgical operating zone to contamination by aerosolized particles in this unfiltered air, PA1 2) the warm, humidified expired air emerging through the upper edge of the mask tends to fog the wearer's eyeglasses and operating microscopes because the relative humidity of the wearer's exhaled air exceeds the dew point of the air in the operating room, impairing the surgeon's visibility, and PA1 3) rebreathing the warm, moist CO.sub.2 -laden air wears on the stamina of the wearer.
The second problem, of fogging eyeglasses and microscopes, has been typically dealt with by affixing adhesive tape along the upper edge of the mask to the wearer's upper nose and cheeks to create a seal. The warm, humid air is then directed out laterally. However, due to perspiration and secretion of skin oils, this tape seal often deteriorates during the course of an operation, with attendant loss of seal and resultant fogging. Additionally, removal of this tape from the skin after each operation can be very uncomfortable and results in painful tape irritation, especially when this may be done several times a day in the course of multiple operations. Moreover, the surgeon is often uncomfortable during surgery, and fatigue tends to occur more quickly.
Such problems with known surgical masks have, in the past, been addressed in several ways. One solution has been to reduce the temperature in the operating room so that the surgeons do not feel as hot and perspire. This solution, however, presents risk of complication for the patient from lowered body temperature, particularly during long operations, and causes discomfort for others in the operating room, such as nurses and anesthesia crew members, who often must wrap themselves in blankets and extra gowns to avoid freezing.
Another solution has been to provide a portable suction device or exhaust fan that can be attached to the surgeon's mask to constantly evacuate exhaled air and draw fresh air into the mask. Such devices have, however, involved many parts and have been rather cumbersome. Further, these types of devices exhaust into the operating room with the concomitant problems of such exhausting.
In recent years, an additional concern has arisen which is just beginning to be addressed by mask manufacturers. The specter of emerging antibiotic-resistant organisms and HIV has introduced the additional consideration of transmission of infectious diseases from the patient to the health care worker. One obvious portal of entry of infective particles to the health care worker is around the loose-fitting edges of a face mask. Mask manufacturers are developing and marketing model masks designed to minimize this risk. These masks entail a much more secure fit of mask to face to eliminate the open spaces around the edges. However, this solution to one problem exacerbates another, in that the tighter-fitting, presumably safer, masks trap more expired air about the face in the enclosed zone between the mask and face. This warm, moist air becomes uncomfortable to the wearer and may even contribute to a sense of fatigue. Furthermore. as the moisture accumulates on the inner surface of the mask, bacterial growth is enhanced and the effectiveness of the mask as a filter diminishes as the breathing passages of the mask material become clogged with moisture.
Outside of the context of surgery, similar problems to those discussed above are experienced where, for whatever reason, one must wear corrective or protective goggles and some manner of protective face mask at the same time, such as for work in dusty environments, where the phenomenon of fogging glasses due to exhaled air tends to occur. In other areas of critical care within a hospital, such as intensive care units, pediatric and neonatal units, transplantation units, chemotherapy units, infectious disease including AIDS units, and other areas where infection of both patient by the care giver and the care giver by the patient is a particular concern, workers have experienced problems with fogging of eyeglasses while wearing protective masks. In research, medical, forensic, or scientific laboratories where protective masks are indicated or desired, either for protection of the worker from experimental agents or protection of the experimental animals and materials from contamination by the worker, similar problems are experienced.
In industrial "clean rooms", such as are required in many high technology fields such as aerospace, computer, electronic, pharmaceutical, medical diagnostic and other biomedical industries, face masks are commonly required of workers to prevent contamination of the product by the worker. Such workers experience the problems enunciated above as well. There is, accordingly, a need for some way of simply and inexpensively minimizing the effects of exhaled air behind masks, such as discomfort and fogged lenses, without the need for lowering room temperatures.
Attempts to satisfy the addressed shortcomings have also had shortcomings. U.S. Pat. No. 3,130,722 to Dempsey, et al., describes an unconventional and impervious mask with fixed vent holes 26 and having an exhaust tube 34 attached to the mask via a nipple connection 30 located in a reinforced section 25 of the mask. The exhaust means in FIG. 1 is a pneumatically-driven exhaust fan. Other exhaust means described in column 4 fail to appreciate the specific relationships between the elements set forth in the present invention..
U.S. Pat. No. 5,054,480 to Bare, et al., describes a headgear to be worn by physicians during a surgical procedure comprising fans for introducing air about the head and face through a complicated system of channels, and an exhaust fan to draw air from the face area. A shroud or hood is draped over the headgear forming a window for viewing. The headgear circulation system is cumbersome to the wearer and difficult to clean for reuse. While such complicated apparatus may be necessary in certain extreme conditions, the vast majority of uses do not require such complexity.
U.S. Pat. No. 4,951,662 to Townsend, Jr., discloses a mask as part of an air circulation loop to create user comfort and eliminate eyeglass fogging. Air chamber tubes 12 and 13 are attached to an air contour plate 11 fitted inside a mask 10, securing the mask to the chamber tubes. The tubes are used to expand the effective volume between the face and mask. A fan 14 located behind the wearer's head recirculates air through the mask in a circular fashion. The fan appears to recirculate exhaled air, as well.
U.S. Pat. No. 4,848,366 to Aita, et al. discloses an impervious surgical mask that may be opaque or clear. The mask has an opening or passageway 23 on both sides. An exhaust tube 26 and a battery-operated exhaust fan 62 is mounted in one opening. The exhaust fan may be mounted directly to the mask. The teaching of Aita, et al. are that the front portion 22 of the mask should be stiff to promote flow of air through the cavity formed by the mask and the face of the wearer. A difficulty with this type of concentrated flow can be the noise level of the air movement. The efficiency of use of the air in scavenging the full mask area can also be a problem.
European Patent Publication 0 018 805, published Nov. 12, 1980 (Douglas) describes an apparatus for controlling exhaled breath from the nose and mouth of a wearer, including a molded, rigid transparent plastic face shield 10 shaped to extend around the lower front portion of the user's face. The shield has a plastic bead 9 to provide an airtight fit. Straps hold the shield in place about the wearer's face. On each side of the shield are outlet coupling members 12 to connect flexible suction conduits 13 at one end. To the other end of the flexible conduit is a motor-driven rotary suction impeller and housing (exhaust fan) to exhaust exhaled breath from the mask. Air enters along the upper edge 11 of the mask.
U.S. Pat. No. 3,890,966 to Aspelin, et al., describes a pervious mask with a sheet of air-impervious sheet material along the upper portion of the mask. The impervious sheet material has slits therein, cut in a manner to direct exhaled air through the slits away from the eyes of the wearer. There is lacking any appreciation for the overall sense of comfort afforded the wearer in the present invention.
All of these problems may be solved by incorporating a simple method to vacuum away, or scavenge, the wearer's expired breath with apparatus readily available in hospital operating rooms. The humid, potentially infectious air may be continuously eliminated from the operative area, and with it the problems of fogging, heat buildup and fatigue, and risk of transmitting infection to or from the patient.